A thin film transistor array substrate is a substrate with arrays of a large number of thin film transistors (TFTs) on a substrate surface, and is widely used in display devices such as liquid crystal display devices, for example. Liquid crystal display devices that use a thin film transistor array substrate are classified as active-matrix liquid crystal display devices. In typical active-matrix liquid crystal display devices, gate bus lines and source bus lines are provided in a grid pattern orthogonal to each other, and thin film transistors are arranged on respective regions partitioned in a matrix by the gate bus lines and source bus lines. The thin film transistor, which is a switching element, is in an ON state when a scan signal is inputted through a gate bus line to the gate electrode of the thin film transistor. When the thin film transistor is in an ON state, an image signal going through each source bus line is transmitted from the source electrode to the drain electrode of each thin film transistor, and then is further transmitted to a pixel electrode. The image signal inputted to each pixel electrode corresponds to a voltage applied between the pixel electrode provided for each pixel and a common electrode shared by all the pixels. In other words, the image signal corresponds to the voltage applied to the liquid crystal in each pixel. The orientation state of the liquid crystals changes based on the voltage applied to the liquid crystals. This makes it possible for a high resolution image to be displayed by controlling the amount of light that can pass through the liquid crystals for each pixel. This active matrix method is commonly used in televisions, monitors, and the like, which perform displays using a large number of pixels.
As described above, there are various types of conductive members provided on a thin film transistor array substrate. Thus, from the viewpoint of ensuring insulation between the different types of conductive members, increasing the pixel aperture ratio (the area ratio of effective display area), and the like, a method is commonly used in which a plurality of conductive members are laminated via an insulating film. In such a case, the respective conductive members are connected to each other, as necessary, via contact holes. For example, in liquid crystal display devices and the like that use a Fringe Field Switching (FFS) mode, a thin film transistor array substrate provided with pixel electrodes and a common electrode is used. In such a thin film transistor array substrate, a configuration is known in which the pixel electrodes and the common electrode are vertically separated by an insulating film.
Various configurations for an electrical path from the drain electrode of a thin film transistor to the pixel electrode on this type of thin film transistor array substrate have been disclosed (for example, see Patent Documents 1 and 2).